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Infection and death from influenza A H1N1 virus in Mexico
The scientific community is aware that pandemics                       fails to protect against the pandemic influenza virus in                  Published Online
                                                                                                                                               November 12, 2009
other than the current influenza A H1N1 outbreak have                  any age group.8 However, data show relative protection                   DOI:10.1016/S0140-
existed throughout history. A characteristic of the H1N1              for people who were exposed to H1N1 strains during                       6736(09)61916-4

pandemic is how fast knowledge evolved, with medical                  childhood before the 1957 pandemic.9                                     See Online/Articles
                                                                                                                                               DOI:10.1016/S0140-
groups confirming or declaring as controversial what                      Influenza surveillance has limitations when we consider                6736(09)61638-X
had been stated weeks after the first outbreaks. This                  the wide spectrum of clinical characteristics;10 many
rapid evolution allowed other groups to establish better              viral or bacterial infections cause the same symptoms.
capabilities to face the pandemic.                                    Surveillance for influenza-like illness is an alternative
  One of the countries facing the first pandemic                       but also has limitations, because not all patients with
wave was Mexico. In The Lancet today, Santiago                        influenza-like illness seek medical attention.11 Moreover,
Echevarría-Zuno and colleagues1 report pandemic data                  during the pandemic, not all patients with influenza-like
from the population of nearly 40 million (out of more                 illness were sampled, especially when all laboratories
than 100 million Mexicans) from all of the country who                have been overloaded. Diagnosis depends on access
attended the clinics of the Instituto Mexicano del Seguro             to laboratories, which is usually centralised. Finally, in
Social (IMSS). Mexican data have been helpful to many                 today’s report, some of the eligible IMSS population
groups, especially in South America. Other countries                  might have attended other health centres, and all these
have gained more time and information to develop                      factors contribute to a bias in incidence rates.
stronger strategies for containment. Since 2000, WHO                     Today’s study might also have had difficulties in
has recommended that all countries start national                     estimating an accurate fatality rate on the basis of
preparedness and response plans before a potential                    the surveillance information collected, for which the
influenza pandemic. Planning in Mexico started in                      denominator could be much higher than the number of
2001,2 and a national drill was tested in 2006.3                      notified cases because of the high prevalence of milder
  At the beginning of the epidemic, Echevarría-Zuno                   cases that did not go to health services. This fatality rate
and colleagues did a rapid influenza test and reverse-
transcriptase PCR on cases and four household or
co-worker contacts of confirmed patients. One thing
not stated is the rapid test results of these contacts
or whether they were asymptomatic. This active
surveillance of contacts uses a lot of human and
economic resources, and is only useful at the start of the
epidemic before sustained transmission is established.                     The printed journal
Rapid influenza testing became controversial because
of uncertainty about the test’s sensitivity to detect
                                                                           includes an image
the A H1N1 subtype of the virus,4,5 but a recent report                    merely for illustration
suggested high sensitivity of the test in the detection of
subtypes.6 The rapid test used in today’s report detects
influenza A and B antigens but cannot discriminate
between influenza A subtypes. Thus the specificity of
this test for the H1N1 pandemic virus is controversial.
Although the test’s limitations were known, during
the pandemic peak (highest prevalence), the positive
predictive value of the test increases,7 which facilitates
management and treatment.
  The likely protection from seasonal influenza vaccine
                                                                                                                                     Reuters




is now more clear than it was previously. This vaccine

www.thelancet.com Published online November 12, 2009 DOI:10.1016/S0140-6736(09)61916-4                                                                               1
    Comment




              could also have been overestimated when the focus was                               1    Echevarría-Zuno S, Mejía-Aranguré JM, Mar-Obeso AJ, et al. Infection and
                                                                                                       death from influenza A H1N1 virus in Mexico: a retrospective analysis.
              on patients in hospital.12                                                               Lancet 2009; published online Nov 12. DOI:10.1016/S0140-
                A significant finding in today’s report was that the                                     6736(09)61638-X.
                                                                                                  2    Perez-Padilla R, de la Rosa-Zamboni D, Ponce de Leon S, et al, for the INER
              infection risk was highest in children, but the disease                                  Working Group on Influenza. Pneumonia and respiratory failure from
                                                                                                       swine-origin influenza A (H1N1) in Mexico. N Engl J Med 2009; 361: 680–89.
              was more severe (ie, higher risk of death) in people
                                                                                                  3    National Committee for Safeness in Health. National exercise to evaluate
              older than 60 years. Additionally, school closures and                                   responses capabilities in a influenza pandemic scenario. Feb 28, 2007.
                                                                                                       http://www.dgepi.salud.gob.mx/pandemia/mini-site/Documentos/
              restrictions of mass gatherings to mitigate the spread of                                Informe-Ejecutivo-200207.pdf (accessed Oct 25, 2009) (in Spanish).
              the epidemic was successful, as has been seen in other                              4    Faix DJ, Sherman SS, Waterman SH. Rapid-test sensitivity for novel
                                                                                                       swine-origin influenza A (H1N1) virus in humans. N Engl J Med 2009;
              countries.13                                                                             361: 728–29.
                Decisions based on preliminary results and limited                                5    Hurt AC, Baas C, Deng YM, Roberts S, Kelso A, Barr IG. Performance of
                                                                                                       influenza rapid point-of-care tests in the detection of swine lineage
              sources have to be made, and sometimes there is no                                       A(H1N1) influenza viruses. Influenza Other Respi Viruses 2009; 3: 171–76.
              time to wait for the pandemic to end to have stronger                               6    Chan KH, Lai ST, Poon LL, Guan Y, Yuen KY, Peiris JS. Analytical sensitivity of
                                                                                                       rapid influenza antigen detection tests for swine-origin influenza virus
              information. Currently, we know that the pandemic                                        (H1N1). J Clin Virol 2009; 45: 205–07.
                                                                                                  7    CDC. Interim guidance for the detection of novel influenza A virus using
              has not reached the dimensions of its predecessor in                                     rapid influenza diagnostic tests. July 29, 2009. http://www.cdc.gov/
              1918, but the scientific knowledge has evolved faster                                     h1n1flu/guidance/rapid_testing.htm (accessed Aug 3, 2009).
                                                                                                  8    Kelly H, Grant K. Interim analysis of pandemic influenza (H1N1) 2009 in
              than before, probably because of global and online                                       Australia: surveillance trends, age of infection and effectiveness of seasonal
              communication.                                                                           vaccination. Euro Surveill 2009; 14: pii: 19288.
                                                                                                  9    Pérez-Trallero E, Piñeiro L, Vicente D, Montes M, Cilla G. Residual inmunity
                                                                                                       in older people against A(H1N1)—recent experience in northern Spain.
              *V Alberto Laguna-Torres, Jorge Gomez Benavides                                          Euro Surveill 2009; 14: pii: 19334.
                                                                                                  10   Carrat F, Vergu E, Ferguson NM, et al. Time lines of infection and disease in
              Virology Department and Influenza Section, US Naval Medical                               human influenza: a review of volunteer challenge studies. Am J Epidemiol
              Research Center Detachment, Lima, Peru (VAL-T); San Marcos                               2008; 167: 775–85.
              University, Lima, Peru (JGB); and General Epidemiology                              11   Laguna-Torres VA, Gomez J, Ocaña V, et al. Influenza-like illness sentinel
                                                                                                       surveillance in Peru. PLoS One 2009; 4: e6118.
              Directorate, Ministry of Health of Peru, Lima, Peru (JGB)
                                                                                                  12   Garske T, Legrand J, Donnelly CA, et al. Assessing the severity of the novel
              laguna_alberto@hotmail.com                                                               influenza A/H1N1 pandemic. BMJ 2009; 339: b2840.
              Our views do not necessarily reflect the official policy or position of the Ministry   13   Gomez J, Munayco CV, Arrasco J, et al. Pandemic influenza in a southern
              of Health of Peru, the Department of the Navy, the Department of Defense, or             hemisphere setting: the experience in Peru from May to September, 2009.
              the US Government. We declare that we have no conflicts of interest.                      Euro Surveill 2009; 14: pii: 19371.




2                                                                          www.thelancet.com Published online November 12, 2009 DOI:10.1016/S0140-6736(09)61916-4

								
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